Dear all,

Sorry for the potentially stupid question, but I'm a complete newbie to D. Why does compiling the following trivial code fail?

import std.stdio;

void main()
{
    writeln(3.14);
}

Error message:

/Library/D/dmd/src/phobos/std/format.d(1601): Error: pure function std.format.FormatSpec!char.FormatSpec.toString cannot call impure function std.format.FormatSpec!char.FormatSpec.toString!(Appender!string).toString
/Library/D/dmd/src/phobos/std/format.d(478): Error: template instance std.format.FormatSpec!char error instantiating
/Library/D/dmd/src/phobos/std/stdio.d(1590):        instantiated from here: formattedWrite!(LockingTextWriter, char, double)
/Library/D/dmd/src/phobos/std/stdio.d(3927):        instantiated from here: write!(double, char)
test1.d(5):        instantiated from here: writeln!double

Cheers,
Michael

On Sunday, 4 October 2020 at 16:48:24 UTC, Michael wrote:
> Dear all,
>
> Sorry for the potentially stupid question, but I'm a complete newbie to D. Why does compiling the following trivial code fail?
>
> import std.stdio;
>
> void main()
> {
>     writeln(3.14);
> }

Works fine for me using DMD 2.094.0 on Linux. What OS and compiler version are you using, and how did you install DMD?

On Sunday, 4 October 2020 at 17:01:44 UTC, Paul Backus wrote:
> On Sunday, 4 October 2020 at 16:48:24 UTC, Michael wrote:
>> Dear all,
>>
>> Sorry for the potentially stupid question, but I'm a complete newbie to D. Why does compiling the following trivial code fail?
>>
>> import std.stdio;
>>
>> void main()
>> {
>>     writeln(3.14);
>> }
>
> Works fine for me using DMD 2.094.0 on Linux. What OS and compiler version are you using, and how did you install DMD?

DMD64 D Compiler v2.094.0
on macOS 10.15.6

On Sunday, 4 October 2020 at 17:05:33 UTC, Michael wrote:
> On Sunday, 4 October 2020 at 17:01:44 UTC, Paul Backus wrote:
>> On Sunday, 4 October 2020 at 16:48:24 UTC, Michael wrote:
>>> Dear all,
>>>
>>> Sorry for the potentially stupid question, but I'm a complete newbie to D. Why does compiling the following trivial code fail?
>>>
>>> import std.stdio;
>>>
>>> void main()
>>> {
>>>     writeln(3.14);
>>> }
>>
>> Works fine for me using DMD 2.094.0 on Linux. What OS and compiler version are you using, and how did you install DMD?
>
> DMD64 D Compiler v2.094.0
> on macOS 10.15.6

I did not use any compiler flags, but just:
dmd test1.d

On Sunday, 4 October 2020 at 16:48:24 UTC, Michael wrote:
> Dear all,
>
> Sorry for the potentially stupid question, but I'm a complete newbie to D. Why does compiling the following trivial code fail?
>
> [...]

I have tried my best to make it fail, but can't. Maybe it's something with the combination of dmd64 and MACOS?

On Sunday, 4 October 2020 at 17:05:33 UTC, Michael wrote:
> On Sunday, 4 October 2020 at 17:01:44 UTC, Paul Backus wrote:
>> On Sunday, 4 October 2020 at 16:48:24 UTC, Michael wrote:
>>> Dear all,
>>>
>>> Sorry for the potentially stupid question, but I'm a complete newbie to D. Why does compiling the following trivial code fail?
>>>
>>> import std.stdio;
>>>
>>> void main()
>>> {
>>>     writeln(3.14);
>>> }
>>
>> Works fine for me using DMD 2.094.0 on Linux. What OS and compiler version are you using, and how did you install DMD?
>
> DMD64 D Compiler v2.094.0
> on macOS 10.15.6

I cannot reproduce locally (macOS 10.15.6 too). How did you install DMD ?

On Sunday, 4 October 2020 at 17:37:52 UTC, Mathias LANG wrote:
> On Sunday, 4 October 2020 at 17:05:33 UTC, Michael wrote:
>> On Sunday, 4 October 2020 at 17:01:44 UTC, Paul Backus wrote:
>>> On Sunday, 4 October 2020 at 16:48:24 UTC, Michael wrote:
>>>> Dear all,
>>>>
>>>> Sorry for the potentially stupid question, but I'm a complete newbie to D. Why does compiling the following trivial code fail?
>>>>
>>>> import std.stdio;
>>>>
>>>> void main()
>>>> {
>>>>     writeln(3.14);
>>>> }
>>>
>>> Works fine for me using DMD 2.094.0 on Linux. What OS and compiler version are you using, and how did you install DMD?
>>
>> DMD64 D Compiler v2.094.0
>> on macOS 10.15.6
>
> I cannot reproduce locally (macOS 10.15.6 too). How did you install DMD ?

I used the dmg file: dmd.2.094.0.dmg

On Sunday, 4 October 2020 at 17:43:13 UTC, Michael wrote:
> On Sunday, 4 October 2020 at 17:37:52 UTC, Mathias LANG wrote:
>> On Sunday, 4 October 2020 at 17:05:33 UTC, Michael wrote:
>>> On Sunday, 4 October 2020 at 17:01:44 UTC, Paul Backus wrote:
>>>> On Sunday, 4 October 2020 at 16:48:24 UTC, Michael wrote:
>>>>> Dear all,
>>>>>
>>>>> Sorry for the potentially stupid question, but I'm a complete newbie to D. Why does compiling the following trivial code fail?
>>>>>
>>>>> import std.stdio;
>>>>>
>>>>> void main()
>>>>> {
>>>>>     writeln(3.14);
>>>>> }
>>>>
>>>> Works fine for me using DMD 2.094.0 on Linux. What OS and compiler version are you using, and how did you install DMD?
>>>
>>> DMD64 D Compiler v2.094.0
>>> on macOS 10.15.6
>>
>> I cannot reproduce locally (macOS 10.15.6 too). How did you install DMD ?
>
> I used the dmg file: dmd.2.094.0.dmg

I reinstalled using the installation script (install.sh) and now it works. Still don't know why the dmg-based intstallation did not work.
https://dlang.org/install.html

Anyway, thanks for your responses!

On Sunday, 4 October 2020 at 18:02:11 UTC, Michael wrote:
> On Sunday, 4 October 2020 at 17:43:13 UTC, Michael wrote:
>> [...]
>> I used the dmg file: dmd.2.094.0.dmg
>
> I reinstalled using the installation script (install.sh) and now it works. Still don't know why the dmg-based intstallation did not work.
> https://dlang.org/install.html
>
> Anyway, thanks for your responses!

I think there might have been a mismatch between the compiler used, and the Phobos library used. This might happen if you used multiple sources for installation, e.g.  brew / macports / dmg (install script is self contained and never affected).